On the link between potential evaporation and regional evaporation from a CBL perspective

The relationship between potential evaporation and actual evaporation was first examined by Bouchet (Proc Berkeley Calif Symp IAHS Publ, 62:134–142, 1963) who considered potential evaporation as the consequence of regional evaporation due to atmospheric feedbacks. Using a heuristic approach, he derived a complementary relationship which, despite no real theoretical background, has proven to be very useful in interpreting many experimental data under various climatic conditions. Here, the relationship between actual and potential evaporation is reinterpreted in the context of the development of the convective boundary layer (CBL): first, with a closed-box approach, where the CBL has an impermeable lid; and then with an open system, where air is exchanged between the CBL and its external environment. By applying steady forcing to these systems, it is shown that an equilibrium state is reached, where potential evaporation has a specific equilibrium formulation as a function of two parameters: one representing large-scale advection and the other the feedback effect of regional evaporation on potential evaporation, i.e. a kind of “medium-scale advection”. It is also shown that the original form of Bouchet’s complementary relationship is not verified in the equilibrium state. This analysis leads us to propose a new and more rational approach of the relationship between potential and actual evaporation through the effective surface resistance of the region.     

Lake surface temperatures in a changing climate: a global sensitivity analysis

We estimate the effects of climatic changes, as predicted by six climate models, on lake surface temperatures on a global scale, using the lake surface equilibrium temperature as a proxy. We evaluate interactions between different forcing variables, the sensitivity of lake surface temperatures to these variables, as well as differences between climate zones. Lake surface equilibrium temperatures are predicted to increase by 70 to 85 % of the increase in air temperatures. On average, air temperature is the main driver for changes in lake surface temperatures, and its effect is reduced by ~10 % by changes in other meteorological variables. However, the contribution of these other variables to the variance is ~40 % of that of air temperature, and their effects can be important at specific locations. The warming increases the importance of longwave radiation and evaporation for the lake surface heat balance compared to shortwave radiation and convective heat fluxes. We discuss the consequences of our findings for the design and evaluation of different types of studies on climate change effects on lakes.     

The flow in a turbulent boundary layer upstream of a change in surface roughness

Modification of a turbulent flow upstream of a change in surface roughness has been studied by means of a stream function-vorticity model.A flow reduction is found upstream of a step change in surface roughness when a fluid flows from a smooth onto a rough surface. Above that layer and above the region of flow reduction downstream of a smooth-rough transition, a flow acceleration is observed. Similar flow modification can be seen at a rough-smooth transition with the exception that flow reduction and flow acceleration are reversed. Within a fetch of –500 < x/z ₀< + 500 (z ₀ is the maximum roughness length, the roughness transition is located at x/z ₀ = 0), flow reduction (flow acceleration) upstream of a roughness transition is one order of magnitude smaller than the flow reduction (flow acceleration) downstream of a smooth-rough (rough-smooth) transition. The flow acceleration (flow reduction) above that layer is two orders of magnitude.The internal boundary layer (IBL) for horizontal mean velocity extends to roughly 300z ₀ upstream of a roughness transition, whereas the IBL for turbulent shear stress as well as the distortion of flow equilibrium extend almost twice as far. For the friction velocity, an undershooting (overshooting) with respect to upstream equilibrium is predicted which precedes overshooting (undershooting) over new equilibrium just behind a roughness transition.The flow modification over a finite fetch of modified roughness is weaker than over a corresponding fetch downstream of a single step change in roughness and the flow stays closer to upstream equilibrium. Even in front of the first roughness change of a finite fetch of modified roughness, a distortion of flow equilibrium due to the second, downwind roughness change can be observed.     

Effects of a dynamic ocean on simulated climate sensitivity to greenhouse gases

The potential effects of a dynamic ocean on climate change are assessed by comparison of a simulation from 1880 into the future by the CSIRO (Mark 2) coupled atmosphere–ocean general circulation model with equilibrium results from a mixed-layer ocean (MLO) version of the model. At 2082, when the effective CO ₂ is tripled, the global warming in the coupled model is barely half the 3×CO ₂ MLO result, largely because of oceanic heat uptake, as diagnosed using an effective heat capacity. The effective ocean depth continues to increase during a further 1700 years with stabilized tripled CO ₂, by which time the mean ocean warming reaches the upper ocean value. Some reduction of the coupled model warming is due to the effective sensitivity (for 2×CO ₂), determined from the radiative response to the forcing, being persistently 0.2 K lower than the MLO model value. A regional energy and feedback analysis shows that this is largely due to an overall equatorward oceanic heat transport anomaly, which reduces the high-latitude warming in the coupled model. The global warming at 3800 is around 95% of the anticipated equilibrium value, which is matched by the result of a simple energy balance model for the approach to equilibrium. The geographical effect of the oceanic heat transport is confirmed using a mixed-layer model with perturbed oceanic heat convergence. The eastern equatorial Pacific warming is enhanced by over 1 K, and rainfall is perturbed in an ENSO-like pattern.     

Atmospheric radiative equilibria in a simple column model

 An analytic radiative-equilibrium model is formulated where both short- and longwave radiation are treated as two-stream (down- and upward) fluxes. An equilibrium state is defined in the model by the vertical temperature profile. The sensitivity of any such state to the model atmosphere’s optical properties is formulated analytically. As an example, this general formulation is applied to a single-column 11-layer model, and the model’s optical parameters are obtained from a detailed radiative parametrization of a general circulation model. The resulting simple column model is then used to study changes in the Earth-atmosphere system’s radiative equilibrium and, in particular, to infer the role of greenhouse trace gases, water vapor and aerosols in modifying the vertical temperature profile. Multiple equilibria appear when a positive surface-albedo feedback is introduced, and their stability is studied. The vertical structure of the radiative fluxes (both short- and longwave) is substantially modified as the temperature profile changes from one equilibrium to another. These equilibria and their stability are compared to those that appear in energy-balance models, which heretofore have ignored the details of the vertical temperature and radiation profiles. Received: 22 December 1995/Accepted: 17 January 1997     

城市中水体布局对大气环境的影响

城市下垫面状况在很大程度上决定城市大气物理环境的特征。在城市区域增加湿地等自然地表有利于城市的减温增湿,促使局地流场发生变化,改善局地微气象条件以及大气物理环境。城市规划大气物理环境多尺度数值模拟系统为城市规划大气物理环境定量评估提供了有效的模拟工具。利用该系统中的城市尺度模式模拟了水体布局为集中型和分散型,水体面积占有率分别为4%、8%、12%和16%条件下,城市大气温度、湿度、风速、城市大气扩散条件的变化及其对城市大气环境的影响,利用北京市城市水体气象观测数据,分析了水体周边和商业区、交通区温、湿度的差异,并对模式模拟结果进行了验证,揭示了城市水体布局对城市大气物理环境影响的可能机制。模拟和观测结果显示,城市水体布局会对城市微气象环境产生一定影响。无论分散型或集中型布局,城市水体面积的增加,都在一定程度上使城市气温降低、湿度增加、平均风速增大。比较而言,分散型水体布局对城市区域微气象环境的影响更为显著。     

水体对气温观测影响的试验分析

2011年项目组设计了浙江省大型水体观测试验方案,选择较大水体,在其上、下风方向特定距离处布设自动气象站,同步观测各站气温,研究气温受水体影响的量化规律。结果表明,水体对周边陆地有白天降温、夜间增温效应,且离水体越近,这种效应越明显;夜间升温效应比白天降温效应显著,3—5月白天降温效应比1—2月明显;在一天中正午的降温影响最大;2km2的水域对下风向100m范围内温度观测有明显影响,100m以远影响不明显。该研究对量化水体影响的范围和量值进行了有益的探索,为气象站科学选址提供了依据。     

我国冬季感热温度分布和人体保暖所需服装量

本文从人体热量平衡观点出发,根据美国著名生物气象学家R·G·Steadman提出的感热温度理论(1—4),计算了我国各地冬季(12—2月)各月的平均感热温度,并讨论了人体保暖所需的服装量。     

Application of a Bivariate Gamma Distribution for a Chemically Reacting Plume in the Atmosphere

The joint concentration probability density function of two reactive chemical species is modelled using a bivariate Gamma distribution coupled with a three-dimensional fluctuating plume model able to simulate the diffusion and mixing of turbulent plumes. A wind-tunnel experiment (Brown and Bilger, J Fluid Mech 312:373–407, 1996), carried out in homogeneous unbounded turbulence, in which nitrogen oxide is released from a point source in an ozone doped background and the chemical reactions take place in non-equilibrium conditions, is considered as a test case. The model is based on a stochastic Langevin equation reproducing the barycentre position distribution through a proper low-pass filter for the turbulence length scales. While the meandering large-scale motion of the plume is directly simulated, the internal mixing relative to the centroid is reproduced using a bivariate Gamma density function. The effect of turbulence on the chemical reaction (segregation), which in this case has not yet attained equilibrium, is directly evaluated through the covariance of the tracer concentration fields. The computed mean concentrations and the O₃–NO concentration covariance are also compared with those obtained by the Alessandrini and Ferrero Lagrangian single particle model (Alessandrini and Ferrero, Physica A 388:1375–1387, 2009) that entails an ad hoc parametrization for the segregation coefficient.     

干旱及半干旱区土壤水热传输模式研究

本文发展了一个干旱地区土壤中水分及热量传输模式。首先从土壤孔隙内水汽运动研究入手,阐明了在土壤深层孔隙中水汽压与液面饱和值之间处在平衡态,而土壤表层则处在非平衡态,因而必要在计算表层蒸发的公式中引入必要的土壤表层阻力,才可使模式简单实用。在此基础上建立了考虑液态水及汽态水运动耦合的多层模式,并用HEIFE沙漠站的资料对模式进行了验证,结果表明此模式较好地再现土壤内及地气界面上的水热交换过程,并且也表明干旱地区土壤中水蒸汽输送对水分平衡及蒸发的计算是重要的。这种模式很易推广到气候研究的干旱土壤下垫面的模式中去。     

On the dynamics of a solitary vortex

The dynamic equilibrium of a solitary vortex of permanent form but arbitrary shape is investigated on a β plane. The vortex is assumed to propagate in the east-west direction. Forces and moments acting on the vortex are computed and the balances between them obtained. The dynamic balances are required for the equilibrium of the vortex and represent the conditions necessary for the existence of a solitary vortex of permanent form. These conditions have two useful expressions, one as integral constraints on the vortex structure and the other as formulas for the propagation speed of the vortex. For the latter, the speed is shown to be proportional to the averaged velocity moment of the vortex and inversely proportional to its averaged relative vorticity. The propagation speed also depends on the size of the vortex; it increases with size for westward propagation and decreases with size for eastward propagation. The effect of current shear on the vortex is also investigated. The results of this study are applicable to the nonlinear barotropic vortex in a nondivergent fluid as well as to the baroclinic vortex, provided that the latter satisfies the quasigeostrophic approximation.     

社交网络中的谣言传播模型与全局动力学分析

传统的谣言传播模型不考虑人群评价对谣言传播的影响,但随着弹幕、评论点赞、评论排序等新机制的广泛应用,人群评论对谣言传播产生了不可忽视的影响.基于上述情况,本文提出一类新型的基于评价机制的ICST谣言传播模型,该模型将人群细化为无知者（I）、评论者（C）、传播者（S）和静默者（T）四类.在验证平衡点存在性的基础上给出了谣言传播阈值R₀,并依据模型的网络结构构造李雅普诺夫函数证明平衡点的全局稳定性.最后,设计仿真算法验证了理论结果的正确性.     

Kinetic limitations on cloud droplet formation and impact on cloud albedo

Under certain conditions mass transfer limitations on the growth of cloud condensation nuclei (CCN) may have a significant impact on the number of droplets that can form in a cloud. The assumption that particles remain in equilibrium until activated may therefore not always be appropriate for aerosol populations existing in the atmosphere. This work identifies three mechanisms that lead to kinetic limitations, the effect of which on activated cloud droplet number and cloud albedo is assessed using a one‐dimensional cloud parcel model with detailed microphysics for a variety of aerosol size distributions and updraft velocities. In assessing the effect of kinetic limitations, we have assumed as cloud droplets not only those that are strictly activated (as dictated by classical Köhler theory), but also unactivated drops large enough to have an impact on cloud optical properties. Aerosol number concentration is found to be the key parameter that controls the significance of kinetic effects. Simulations indicate that the equilibrium assumption leads to an overprediction of droplet number by less than 10% for marine aerosol; this overprediction can exceed 40% for urban type aerosol. Overall, the effect of kinetic limitations on cloud albedo can be considered important when equilibrium activation theory consistently overpredicts droplet number by more than 10%. The maximum change in cloud albedo as a result of kinetic limitations is less than 0.005 for cases such as marine aerosol; however albedo differences can exceed 0.1 under more polluted conditions. Kinetic limitations are thus not expected to be climatically significant on a global scale, but can regionally have a large impact on cloud albedo.     

Quasigeostrophic, ellipsoidal vortices in a stratified fluid

As a very simple model of some of the lens-like vortices of Mediterranean origin that drift in the eastern North Atlantic, we consider an ellipsoidal volume of uniform potential vorticity embedded in an otherwise quiescent, uniformly stratified fluid of infinite extent. We show that, under the quasigeostrophic approximation, such a vortex is a steadily rotating equilibrium solution and obtains its rotation rate as a function of the lengths of the principal axes. We also determine the dispersion relations for normal modes propagating on the ellipsoid. We find that unstable eigenmodes exist over a considerable range of the geometrical parameters that characterise the ellipsoid.     

Spin-up behavior of soil moisture content over East Asia in a land surface model

This study presents an investigation of the spin-up behavior of soil moisture content (SMC) and evapotranspiration (ET) in an offline Noah land surface model (LSM) for East Asia, focusing on its interplay with the Asian monsoon. The set of 5-year recursive runs is conducted to properly assess the spin-up behavior of land surface processes and consists of simulations initialized with (1) a spatially uniform soil moisture, (2) NCEP GDAS soil moisture data, and (3) ECMWF ERA-Interim soil moisture data. Each run starts either after or before the summer monsoon. Initial SMCs from GDAS and ERA-Interim data significantly deviate from the equilibrium state (spin-up state) with the given input forcing even though the same equilibrium is reached within 3-year spin-up time, indicating that spin-up of land surface process is necessary. SMC reaches the equilibrium much quickly when (1) the consistent LSMs have been used in the prediction and analysis systems and (2) the spin-up simulation starts before the onset of heavy rainfall events during summer monsoon. For an area with heavy monsoon rainfall, the total column SMC and ET spin up quickly. The spin-up time over dry land is about 2–3?years, but for monsoon rainfall area decreases dramatically to about 3?months if the spin-up run starts just before the onset of monsoon. Further scrutiny shows that the spin-up time is well correlated with evaporative fraction given by the ratio between the latent heat flux and the available energy at the land surface.     

Parameterization of meridional energy flux in a one-dimensional climate model

Summary The zonally averaged meridional energy transport is parameterized in terms of the zonally averaged temperature gradient and its radiative equilibrium value. Two climate regimes are identified: radiative equilibrium and isothermal climates. The transport and temperature gradient are intermediate between corresponding quantities of these two climates. The parameterization assumes a linear increase of transport as temperature gradient departs from its radiative equilibrium value. The parameterization is formulated using a one-dimensional climate model. Ice-albedo feedback provides the mechanism for climate changes. The parameterization works well for climates associated with seasonal changes.

---

Parameterisierung des meridionalen Energiestromes in einem eindimensionalen Klimamodell

Zusammenfassung Der zonal gemittelte, meridionale Energietransport wird in Abhängigkeit vom zonal gemittelten Temperaturgradienten und seinem Strahlungsgleichgewicht parameterisiert. Zwei Klimaregime können identifiziert werden: Strahlungsgleichgewicht und isothermes Klima. Der Transport und der Temperaturgradient befinden sich zwischen den korrespondierenden Werten dieser zwei Klimate. Die Parameterisierung nimmt eine lineare Zunahme des Transportes mit der Abweichung des Temperaturgradienten vom seinem Strahlungsgleichgewichtswert an. Die Parameterisierung wird unter Verwendung eines eindimensionalen Klimamodelles formuliert. Die Eis-Albedo-Rückkopplung liefert den Mechanismus für Klimadnderungen. Die Parameterisierung funktioniert gut fur Klimate, welche jahreszeitliche Anderungen beinhalten.

---

---

With 4 Figures     

基于CGE模型的碳税政策模拟——以广东省为例

科学设置碳税政策是控制二氧化碳排放量和推动能源结构优化的重要基础,文中以广东省为例,利用2012年的广东省投入产出表、广东统计年鉴、广东财政年鉴、中国统计年鉴等数据构建社会核算矩阵,通过构建静态的可计算一般均衡模型（CGE),进行区域的碳税政策模拟,分析不同程度的碳税税率对化石能源消费量及各宏观经济变量的影响。结果表明：征收碳税对减排效果有明显的正向作用,当碳税水平为60元/t时,广东省减排效果为3.90%;在碳税定价上,60元/t较为合适;减排贡献率最高的化石能源为煤炭,其次为石油,最低为天然气;碳税冲击下能源消费量下降,最明显的为煤炭,其次是火电;碳税冲击也能显著减少各部门对煤炭的消费量;碳税政策对广东省GDP和社会福利有负向作用,但对总体碳排放强度有正向作用。未来广东省应严格控制煤炭消费量,同时对火电部门进行低碳改造。     

Strong wind structure near a sea-land roughness discontinuity

During the winters of 1977 and 1978, the Centre Scientifique et Technique du Bâtiment (CSTB) carried out a study on the Atlantic littoral in order to determine the modifications to which an air flow is subjected in the surface boundary layer, as it crosses a sea-land discontinuity. The study shows that, in the zone directly leeward of the shore, the structure of the flow is strongly influenced by the acceleration effect of the dune and by the magnitude of the land roughness. In particular, there is a significant disturbance of the logarithmic equilibrium of the air flow.     

Including the Urban Canopy Layer in a Lagrangian Particle Dispersion Model

Boundary-Layer Meteorology - When wind blows over the ocean, short wind-waves (of wavelength smaller than 10 m) are generated, rapidly reaching an equilibrium with the overlying turbulence (at...     

A mixed-flux equilibrium asynchronous coupling scheme for accelerating convergence in ocean-atmosphere models

A coupled atmosphere/mixed-layer ocean energy balance model of intermediate complexity is used to examine the feasibility of a technique to accelerate the model's convergence rate while using equilibrium asynchronous coupling (EAC). EAC consists of an iterative sequence of integrations of an atmospheric model driven to equilibrium with fixed SSTs, the output of which is used to drive an ocean model to equilibrium. In an attempt to accelerate a radiatively perturbed climate to its final equilibrium state, we superimpose on the EAC scheme a mixed-flux condition, in which a portion of the turbulent air-sea heat flux from the most recent atmospheric leg is used in the present oceanic integration. In sensitivity tests using enhanced insolation, this mixed-flux approach strongly hastens the model's convergence rate, whose acceleration is regionally dependent: the tropics show the strongest sensitivity to the mixed-flux condition, while polar regions are least affected. This geographic variation stems from the presence of polar sea-ice, which promotes a temperature inversion and thereby causes a seasonal change in the sign of the total turbulent air-sea heat flux. Potential applications and limitations of this accelerated EAC method are also discussed.